"They described a transit-time tube in which the three characteristic features; velocity modulation, phase focusing, and energy transfer were designed to occur in three separate regions, an arrangement which is also characteristic of a klystron. Further they demonstrated, in my opinion for the first time, that it is necessary, in order to achieve high RF power output, to use a linear electron beam, and that the beam must be positioned in such a way as to prevent the electrons from landing on RF electrodes - they must only be allowed to penetrate the fringe field of the RF electrodes, finally landing on a separate electrode, now called the collector. This arrangement made it possible to separate high frequency from beam guiding electrodes, thus permitting the use of high power electron beams" (Sarkar, History of Wireless).

"which outlined the fundamental working principles of the klystron tube, a high power microwave oscillator, used to provide the transmitter power in the newly developed radar equipment. Leaving Arsenjeva in Russia, he later moved to the UK to continue development work on the klystron with Standard Telephones and Cables (STC), the UK arm of ITT. The day before England went to war with Germany Heil slipped out of the country returning to Germany to continue his work at Standard Electric Lorentz (SEL), ITT's German arm in Berlin. Heil's klystrons, known as "Heil's Generators", became key components in Germany's World War II radars."

"After the war Heil's name appeared on an FBI list of Germans accused of war crimes. He was brought to the US by the military and worked at Wright Patterson Air Force Base. Subsequently he formed his own company and carried out intensive research the physiology of the human ear and sound generation by small animals which he applied to the design of sound transducers. His 1973 patent for the Heil Air Motion Transformer (AMT) made him well known to HiFi buffs.